The invention relates to a device for recovery of waste heat generated during operation of an internal combustion engine and especially a diesel engine. The invention can be applied in vehicles and especially in heavy-duty vehicles such as trucks, buses and construction equipment (such as wheel loaders, excavators and articulated haulers). Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as buses and construction equipment. The invention further relates to an engine system comprising the waste heat recovery device. The invention further relates to a vehicle comprising the engine system for recovery of waste heat of an internal combustion engine comprised in the vehicle. The invention further relates to a method for recovery of waste heat generated during operation of an internal combustion engine.
The waste heat recovery device comprises a thermodynamic engine configured for recovery of waste heat, especially from the exhaust gas stream. The thermodynamic engine comprises a working fluid circulation circuit. More specifically, the thermodynamic engine is configured for converting thermal energy of a gaseous phase working fluid into kinetic energy, and may be constituted by a Rankine cycle engine.
The working fluid of a waste heat recovery device based on a Rankine cycle usually cycles through four stages. In a first stage the liquid working fluid is pumped from low to high pressure. In the subsequent stage, the high pressure liquid working fluid is heated, e.g. by an external heat source, and thereby converted into its gaseous phase. In the next stage, the gaseous phase working fluid expands in an expander engine, for example a displacement expander, such as a piston engine, and/or a turbine. In its last stage, the working fluid is cooled down in a condenser and converted back to its liquid phase.
Usually, in a vehicle, the expander engine may either be connected to a generator for generating electric energy or to a drivetrain of a vehicle thereby acting as auxiliary power unit for the internal combustion engine.
In the condenser, the working fluid needs to be cooled below a condensing temperature of the working fluid. The cooling possibilities in a vehicle are however limited and in many applications already exhausted for cooling the internal combustion engine during high load ICE operation modes and in hot climates. Even if it seems possible to increase the fan size and/or the fan power, this also results in higher fuel consumption and/or a higher air resistance of the vehicle. Both of which should be avoided.
US 2012/0198840 discloses a device for recuperation of waste heat of an internal combustion engine, wherein a steam circuit is connected to a cooling circuit of the internal combustion engine for cooling of the working fluid in the steam circuit. More specifically, the cooling circuit of the ICE is branched off at the radiator outlet.
When there is a low or medium demand of power to the vehicle, the thermodynamic engine may be cooled from the radiator out utilising a low condensing temperature which gives a high Rankine efficiency. However, when there is a high demand of power to the vehicle and possibly also a high ambient temperature, the cooling efficiency of the vehicle is too low for using the radiator out for the thermodynamic engine, which may lead to a low Rankine efficiency.
It is desirable to provide a waste heat recovery device, which creates conditions for an improved recovery of waste heat, especially during high load ICE operation modes and in hot climates.
A waste heat recovery device according to an aspect of the invention comprises a first means for providing a first coolant from a first source for heat exchange with the working fluid in the working fluid circulation circuit, and at least one further means for providing a further coolant from a further source for heat exchange with the working fluid in the working fluid circulation circuit, wherein the further source is at different heat level than the first source during operation of the internal combustion engine.
The term “means for providing a . . . coolant” may for example comprise a conduit for the working fluid and some kind of connection means for operatively connecting the conduit to the source. Further, the term “means for providing a . . . coolant” may for example comprise a valve or similar for controlling a coolant flow from the source.
Further, the term “source” should not be interpreted as limited to a component capable of providing the required cooling during operation of the internal combustion engine, but to comprise for example a part of a component or conduit, a working fluid or position of a component or conduit. Further, the first source and the further source may be formed by two separate components or working fluids or may be formed by the same component or working fluid provided that the criteria that the two sources are configured to be on different heat levels is fulfilled.
Preferably, the first source is associated to the internal combustion engine. Further preferably, the further source is associated to the internal combustion engine. The wording “associated to the internal combustion engine” should not be interpreted to be limited to that the source is an integral part of the internal combustion engine itself, but to comprise also systems and components operatively connected to the internal combustion engine or at least which functioning has an impact on the operation of the internal combustion engine or vice versa.
By the provision of a waste heat recovery device, which comprises the first means for providing a first coolant from a first source and the further means for providing a further coolant from a further source, which sources are on different heat levels, the advantage that the thermodynamic engine may be provided with different cooling capability depending on the specific conditions, such as internal combustion engine operational conditions, atmospheric conditions, cooling requirements for other systems etc. Further, the waste heat recovery device creates conditions for a cost effective and small-sized cooling arrangement.
Further, using coolant of at least two different temperatures allows for an increased cooling capacity of the vehicle.
The provision of a waste heat recovery device, which comprises the first means for providing a first coolant from a first source and the further means for providing a further coolant from a further source, which sources are on different heat levels, creates conditions for providing a relatively cold coolant and/or a relatively warm coolant and/or a mixture of cold and warm coolant to the thermodynamic engine.
This enables that during low or normal ICE operation modes, the thermodynamic engine is cooled by cold coolant and thus may be cooled to a low temperature thereby increasing the efficiency of the energy conversion. During high load ICE operation modes or if the internal combustion engine is operated at high ambient temperature, the cold ICE coolant is required for cooling the internal combustion engine. In this case, the thermodynamic engine may be cooled by the warm (ICE) coolant returning from the internal combustion engine, which may decrease the energy conversion efficiency of the heat recovery assembly, but increases the temperature of the ICE coolant at the inlet of the ICE cooling device, which in turn increases the cooling capacity of the vehicle.
In the following the term “ICE operation modes” is used as abbreviation of“internal combustion engine operation modes”:
i. “High load ICE operation modes” are defined as ICE operation modes, where the driving situation requires a lot of driving force, e.g. running uphill or accelerating.
II “Normal load ICE operation modes” are defined as ICE operation modes, where the vehicle is neither substantially accelerating nor substantially decelerating, e.g. the vehicle is running at constant speed on a high way.
III “Low load ICE operation modes” are defined as ICE operation modes, where the vehicle requires little driving force, e.g. when the vehicle is running downhill or decelerates.
IV. “No load ICE operation modes” are defined as ICE operation modes, where the internal combustion engine is stopped.
Usually, the ICE cooling circuit comprises an ICE coolant cooler, preferably a radiator, for providing cold ICE coolant, an ICE coolant supply duct for supplying the cold ICE coolant from the cooler to the internal combustion engine, an ICE coolant return pipe for returning warm ICE coolant from the internal combustion engine to the cooler and a pump for transportation of the ICE coolant. Preferably, the pump is arranged at the ICE coolant supply duct.
The waste heat recovery device is preferably adapted to convert thermal energy of a waste heat source of the internal combustion engine into kinetic and/or electric energy.
According to one embodiment, the first coolant providing means is configured for providing the working fluid circulation circuit with the first coolant from a cooling arrangement of the internal combustion engine. By using the ICE coolant, an additional coolant circuit for the working fluid circulation circuit is not necessary, which in turn reduces the number of parts in the vehicle and allows for an increased and efficiency-improved cooling concept.
Preferably, the first coolant providing means is configured for being connected to a coolant conduit of the cooling arrangement of the internal combustion engine in a position downstreams the internal combustion engine and upstreams a radiator in the cooling arrangement of the internal combustion engine.
According to a further embodiment, the further coolant providing means comprises a second coolant providing means configured for providing the working fluid circulation circuit with a second coolant from a cooling arrangement of the internal combustion engine. By using the ICE coolant for both the first coolant providing means and the further coolant providing means, an additional coolant circuit for the working fluid circulation circuit is not necessary, which in turn reduces the number of parts in the vehicle and allows for an increased and efficiency-improved cooling concept.
Preferably, the second coolant providing means is configured for being connected to a coolant conduit of the cooling arrangement of the internal combustion engine in a position downstreams of a radiator in the cooling arrangement of the internal combustion engine and upstreams of the internal combustion engine.
For example, when there is a low or medium demand of power to the vehicle, the thermodynamic engine may be cooled from the radiator out utilising a low condensing temperature which gives a high Rankine efficiency. When there is a high demand of power to the vehicle and possibly also a high ambient temperature so that the cooling efficiency of the vehicle is too low for using the radiator out, then the condensing temperature is increased and the coolant is taken from the engine out.
For providing ICE coolant of at least two different temperatures, the system preferably comprises a cold ICE coolant supply branch branching off from the ICE coolant supply duct, preferably upstream of the pump, and/or a warm ICE coolant supply branch branching off from the ICE coolant return duct.
According to a further embodiment, the further coolant providing means comprises a third coolant providing means configured for providing the working fluid circulation circuit with a third coolant from a component positioned for heat exchange with ambient air, which component is separate from a cooling arrangement of the internal combustion engine. For example, the heat exchange component may be formed by a cooling device positioned adjacent the radiator in the internal combustion engine cooling circuit.
The third coolant providing means may be an alternative to the second coolant providing means or the waste heat recovery device may comprise both the second coolant providing means and the third coolant providing means.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.